JimGnitecki
Member
- Joined
- Mar 28, 2010
- Messages
- 1,258
I am experiencing an interesting unexpected COAL issue due to the Dillon 9mm bullet seating die bought with my Dillon XL750.
I have been finding that despite all my efforts to consistently apply the same stroke with the same pressure on every stroke of the press handle, I am getting some variation in cartridge overall length, when I measure from base of cartridge to tip of the bullet hollowpoint (I have no tool to measure from base of cartridge to ogive for this 9mm pistol cartridge). In extreme cases, the difference between longest and shortest COAL hits 0.010". Yet, the actual performance of the cartridges i am loading, with 5 shot groups at 25 yards, is as good as 0.81 inches.
I have examined the fit of the 115g Hornady HAP 0.355" 9mm bullet with the reversible seating insert inside the Dillon die, and see the problem: Neither end of the insert can control the bullet via its ogive. Rather, each end seats the bullet via controlling the TIP of the bullet. This is because the only contact between the insert and the bullet occurs right at the tip of the hollowpoint. i.e. the "recess", at either end of the reversible insert, is too wide, so the bullet "bottoms" onto the flat END of the recess. And, I suspect, each hollowpoint bullet tip "crushes" slightly by a differing amount, because the hollowpoint is indeed "hollow" and therefore malleable.
The ogive of the jacketed hollowpoint HAP bullet is basically a straight (i.e. non-curved) truncated cone shaped ogive topped by a hollowpoint. So, a seating insert that can capture and control the ogive could create a very consistent "Overall Length" if measured from the base of the cartridge to the point of ogive contact, and any variation in the TIP of the bullet height would basically be of no consequence since the tip portion does not contact the chamber lead or rifling, so it does not affect pressure produced and therefore will have no impact on bullet speed.
But since the Dillon insert grabs the tip, my theory is that the COAL I get by measuring with my digital caliper, which can only measure from base to tip (not to ogive), varies with the varying OAL length of each bullet tip and by the degree of deformative "crushing" of the tip during seating.
I did a sample analysis of the bullet OAL, and got these results:
Average OAL = 0.5393"
Std Dev = .0019"
Max height = .5445"
Min height = .5375"
Extreme spread = .007"
This explains the up to .010" extreme spread i am getting on the digital caliper. Only .003" is due to my setup and / or inconsistency of pressure. Most of it is due the variation in bullet OAL.
So, I think I need to measure base to ogive, but I don't know where i could get such a gage to sue with my caliper.
A more practical solution seems to be to simply buy a seating die that does capture the ogive versus the tip of the bullet. This solution would not enable me to measure more accurately with my caliper, BUT it would actually make the TRUE COAL (i.e. base to ogive) significantly more consistent, since the deformable and variable height tip of the bullet would no longer be controlling the actual bullet placement within the case.
Dillon does not appear to offer such a seating insert or complete die.
I have ordered a 9mm Redding Competition bullet seating die. That die has a couple of nice features:
- Its shape, at least the one I saw being used in .45 ACP, works properly with a straight cone shaped ogive hollowpoint bullet, capturing the ogive versus the tip
- It has a self-retracting "sleeve" that guides the combination of case and unseated bullet perfectly coaxially aligned into the seating insert
- Its seating height is controlled by a micrometer knob that allows accurate adjustment to a precision of .001"
- It is designed to work in progressive presses as well as single stage presses.
I am hoping this will make the true COAL of my cartridges more consistent.
Jim G
I have been finding that despite all my efforts to consistently apply the same stroke with the same pressure on every stroke of the press handle, I am getting some variation in cartridge overall length, when I measure from base of cartridge to tip of the bullet hollowpoint (I have no tool to measure from base of cartridge to ogive for this 9mm pistol cartridge). In extreme cases, the difference between longest and shortest COAL hits 0.010". Yet, the actual performance of the cartridges i am loading, with 5 shot groups at 25 yards, is as good as 0.81 inches.
I have examined the fit of the 115g Hornady HAP 0.355" 9mm bullet with the reversible seating insert inside the Dillon die, and see the problem: Neither end of the insert can control the bullet via its ogive. Rather, each end seats the bullet via controlling the TIP of the bullet. This is because the only contact between the insert and the bullet occurs right at the tip of the hollowpoint. i.e. the "recess", at either end of the reversible insert, is too wide, so the bullet "bottoms" onto the flat END of the recess. And, I suspect, each hollowpoint bullet tip "crushes" slightly by a differing amount, because the hollowpoint is indeed "hollow" and therefore malleable.
The ogive of the jacketed hollowpoint HAP bullet is basically a straight (i.e. non-curved) truncated cone shaped ogive topped by a hollowpoint. So, a seating insert that can capture and control the ogive could create a very consistent "Overall Length" if measured from the base of the cartridge to the point of ogive contact, and any variation in the TIP of the bullet height would basically be of no consequence since the tip portion does not contact the chamber lead or rifling, so it does not affect pressure produced and therefore will have no impact on bullet speed.
But since the Dillon insert grabs the tip, my theory is that the COAL I get by measuring with my digital caliper, which can only measure from base to tip (not to ogive), varies with the varying OAL length of each bullet tip and by the degree of deformative "crushing" of the tip during seating.
I did a sample analysis of the bullet OAL, and got these results:
Average OAL = 0.5393"
Std Dev = .0019"
Max height = .5445"
Min height = .5375"
Extreme spread = .007"
This explains the up to .010" extreme spread i am getting on the digital caliper. Only .003" is due to my setup and / or inconsistency of pressure. Most of it is due the variation in bullet OAL.
So, I think I need to measure base to ogive, but I don't know where i could get such a gage to sue with my caliper.
A more practical solution seems to be to simply buy a seating die that does capture the ogive versus the tip of the bullet. This solution would not enable me to measure more accurately with my caliper, BUT it would actually make the TRUE COAL (i.e. base to ogive) significantly more consistent, since the deformable and variable height tip of the bullet would no longer be controlling the actual bullet placement within the case.
Dillon does not appear to offer such a seating insert or complete die.
I have ordered a 9mm Redding Competition bullet seating die. That die has a couple of nice features:
- Its shape, at least the one I saw being used in .45 ACP, works properly with a straight cone shaped ogive hollowpoint bullet, capturing the ogive versus the tip
- It has a self-retracting "sleeve" that guides the combination of case and unseated bullet perfectly coaxially aligned into the seating insert
- Its seating height is controlled by a micrometer knob that allows accurate adjustment to a precision of .001"
- It is designed to work in progressive presses as well as single stage presses.
I am hoping this will make the true COAL of my cartridges more consistent.
Jim G